Abstract The accumulated case studies in the Sociology of Scientific Knowledge have been taken to establish the Strong Programme's thesis that beliefs have social causes in contradistinction to psychological ones. This externalism is essentially a commitment to the stimulus control of behaviour which was the principal tenet of orthodox Skinnerian Behaviorism. Offered as ?straight forward scientific hypotheses? these claims of social determination are asserted to be ?beyond dispute?. However, the causes of beliefs and especially their contents has also been the (...) subject of intense study in the quite different domain of cognitive science where internal states, images, rules, representations and schemas are postulated as explanatory constructs. Such explanations which postulate mental states are described by Bloor as infected by the ?disease? of ?psychologism? and Bloor has defined his Strong Programme in terms of its diametrical opposition to mentalistic theories. For example, Bloor has explicitly endorsed the Behaviourist rejection of mental representations such as images. Accordingly, a direct comparison of these radically divergent approaches to a common subject matter is of considerable interest. The paper attempts to reveal the unnoticed enormity and recidivism of the sociological programme, and how its vulnerability is betrayed in Bloor's response to criticism on central issues. (shrink)